Abstract: Light Dependent Resistors (LDR's) are used together with a differential amplifier and a plurality of reference resistors to replace conventional analog potentiometer controls and thus offer digital activation and programmability to a traditional style vacuum tube preamplifier.

Abstract: A power supply for use with a musical amplifier includes two user-selectable rectifiers for variously enhancing sound generated by a musical instrument such as a guitar, or by recorded musical material which in either case consists of electrical signals applied to a vacuum tube amplifying apparatus. The first of two rectifiers comprises one or more thermionic vacuum tube devices, depending upon power needs, while the second rectifier is comprised of solid-state silicon diodes. A switch circuit enables the user to select which of the two rectifier devices is better suited to the contemporaneous use of the amplifier.